1. Field of the Invention
The present invention relates, to an automatic original feeding device provided in an image forming apparatus, and more particularly, to an automatic original feeding device with a feed roller for delivering originals to a position for exposure.
2. Description of the Related Art
Modern image forming apparatuses, such as copying machines, are expected to be versatile or of high performance. Therefore, these apparatuses are often provided with an automatic original feeding device, in which originals are automatically set in an exposure position on an original table, and are automatically discharged from the table after exposure. A typical example of ,the feeding device of this type is disclosed in U.S. patent application Ser. No. 372,567. This device uses only feed rollers as the transfer means at the end of the original table, instead of using a conveyor belt. More specifically, according to this original feeding device, the feed rollers are arranged at the rear end of the original table so that the originals can be transported between the rollers and the table. Each original, picked up from an original tray by means of pick-up means, is fed forward by the feed rollers, and is then moved back a short distance so that it abuts against a stopper at the rear end of the original table. Thus, the original is set in the exposure position on the table. After it is exposed, the original taken out from the original table by means of the same feed rollers, and is then discharged onto an original receiving tray by means of discharge rollers, or transported toward aligning rollers by means of reversal rollers.
In the automatic original feeding device constructed in this manner, however, even when the original from the feed rollers reach the discharge rollers or the reversal rollers, its end portion is still held between the original table and the feed rollers, and is subjected to a conveying force from the feed rollers. Therefore, the feed rollers must be driven at the same speed as the discharge rollers or the reversal rollers. If these rollers are driven by means of a common motor, however, a complicated, large-sized power transmission mechanism is required, constituting a hindrance to reduction of the size, weight, and manufacturing cost of the device. If the rollers are driven by means of separate motors, on the other hand, different characteristics are expected of the drive sources for the feed rollers, which require a high rotating speed for high-speed operation, and for the discharge rollers or the reversal rollers, which require a low rotating speed for reliable discharge of the original paper. Thus, it is difficult to equalize the respective transportation speeds of the rollers, and the power transmission mechanism is complicated. If the drive speed of the discharge rollers is lower than that of the feed rollers, for example, the original will be bent within the transfer path between the rollers, and be doubled or damaged. If the drive speed of the discharge rollers is higher than that of the feed rollers, on the other hand, the original will be pulled by the rollers in the transfer path between them, so that it will possibly be torn or stained with rubbing marks of the rollers. This also applies to the case of the reversal rollers. The feed rollers are always on the original table, and, at the time of delivery of the original, are engaged in the discharge of the original until the trailing end of the original passes the feed rollers entirely. After the image forming operation is finished, therefore, a subsequent original cannot be fed onto the original table before the trailing end of the preceding original passed the feed rollers. Thus, the original feeding operation, and therefore, the image forming operation, cannot be performed at high speed.